This invention relates generally to hypodermic injection devices, and more particularly to reusable hypodermic jet injectors, or needleless injectors, in which a dosage of medicine and a powering charge are contained within a disposable ampule.
Hypodermic injection devices capable of administering a dosage of medicine in the form of a fine, high-velocity jet delivered with sufficient force as to pass through skin tissue without the need of a hypodermic needle have been known since at least the 1960s. Perhaps the widest application of jet injectors is in the administration of insulin to individuals afflicted with diabetes, although such devices are also known for use in vaccinations as well as the administration of vitamins, anesthetics and other medicines in liquid form. Examples of jet injectors employing disposable ampules are disclosed in the following patents:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,335,722 Lowry et al. Aug. 15, 1967 4,089,334 Schwebel et al. May 16, 1978 4,124,024 Schwebel et al. Nov. 7, 1978 4,518,385 Lindmayer et al. May 21, 1985 4,940,460 Casey et al. Jul. 10, 1990 5,312,335 McKinnon et al. May 17, 1994 ______________________________________
Cost is normally a factor in the selection of any disposable device, and the cost of a disposable ampule is directly affected by the amount of material required for a particular ampule design as well as by manufacturing costs. In a number of the devices disclosed in the above patents a disposable ampule extends out of the forward end of the injector and, as such, must be designed to withstand the high internal pressures developed during injection. For example, disposable ampules have been made according to the principles of U.S. Pat. No. 4,089,334 to Schwebel et al. using polycarbonate, and a wall thickness of 0.100" has been found necessary with such a material. Reinforcement of the exposed exterior portion of an ampule as shown in U.S. Pat. No. 4,124,024 to Schwebel et al. can provide the strength required to withstand the pressures encountered during an injection, but at the cost of additional material incorporated into the ampule for reinforcement.
Lowry et al. discloses a disposable ampule having a stainless steel nose piece over the front end of a plastic sleeve, with the complete ampule except for the tip of the nose piece enclosed within the bore of the jet injector. Lowry et al. indicates a maximum thickness of about 0.020" for the stainless steel nose piece, and a greater thickness for the plastic sleeve. The ampule does not include a propellant charge; instead, a stopper of neoprene rubber or like elastomer is exposed at the rear of the ampule and is contacted from the rear by a piston which is forced forward into the ampule under pressure developed from the ignition of a propellant charge contained in a separate part of the hypodermic device.
Manufacturing concerns also come into play in connection with the cost of a disposable ampule. For example, the cycle time for a molding operation increases as a function of increased wall thickness and has a corresponding impact on labor costs and operating expenses.
In addition, we have discovered that injection molding of plastic ampules can be made more efficient by molding the ampules with draft angles, i.e., slightly tapered surfaces as opposed to uniform cylindrical surfaces. Draft angles on the inside and outside surfaces of an ampule will facilitate the separation of a newly molded ampule from an outer mold section or sections as well as from a core pin or insert or other inner mold part. It is further believed that such a construction will eliminate the need for a mold release, and thereby eliminate the associated material cost as well as the time required to apply the mold release to the mold surfaces and to thereafter remove all residual mold release from the molded ampule to prevent contamination.
Lindmayer et al. discloses a syringe for a needleless injector in which the barrel of the syringe tapers slightly from front to rear and the injector barrel in which it fits is tapered internally to match the taper of the syringe barrel in order to use a thin-walled syringe barrel which is capable of resisting the high pressures required to create a high-velocity jet. The patent refers, without explanation or illustration, to a barrel and plunger tapered slightly for insertion into a similarly tapered casing of an injector, but the syringe plunger as disclosed is an elongated hard plastic body described as a cylindrical body with a conical front end for abutting the conical front end of the syringe barrel. Internally, the syringe barrel, which may be formed of polypropylene, similarly appears uniformly cylindrical in shape except for its conical front end. Without a draft angle on the inside wall surface of an ampule, however, injection molding of the ampule is made more difficult and consequently more expensive.
There is also an ever-increasing need for devices for rapidly and easily but very accurately filling jet injectors with a required medicine dosage, especially for home health care. Injectors suited for self-administration of medicine in a home care setting are desirable from a cost standpoint as well as from the standpoint of patient convenience, especially for long-term care which would otherwise necessitate frequent appointments with medical personnel. Cost constraints practically dictate reusable jet injectors, because it is impractical to dispose of a complete device after one use, and reusable jet injectors need to be filled prior to each use.
Some reusable injectors permit filling of medicine directly into an injection chamber, while others are designed to receive a prefilled ampule. After an injection with the former type, the injection chamber and any passageways leading to it from a supply vial inevitably contain some residual amount of medicine which can be difficult to remove. Periodic cleaning is typically required with such injectors, as exemplified by the Medi-Jector.RTM., commercially available from Derata Corporation. Without proper cleaning, the residual amounts of medicine can lead to complications, particularly when different types of medicine are to be injected, as is fairly common in insulin administration regimens.
Patients are more likely to accept, and properly use, a jet injector that is simple to set up for use and that requires little or no cleaning after use. Prefilled ampules can help meet these criteria, but it is not practical to maintain a large inventory of ampules prefilled with various different amounts of different types of medicine. Physicians commonly prescribe different dosages of medicine for different medical conditions including the type and severity of an illness as well as the age and weight of an individual patient. In such situations it is highly desirable to have a single type of ampule that can accommodate different dosages. It would be most advantageous for patients in home care settings to be able to quickly and confidently fill such an ampule with a prescribed dosage from a conventional medicine vial, without help from medically trained personnel. However, this would require a filling mechanism that is fast and simple to use and still capable of precise measurement by untrained individuals.
Casey et al. discloses a patient-fillable ampule for a hypodermic injection device which can accommodate different dosages and which is filled via an adapter from a separate medicine bottle. The injection device assembly comprises a sleeve attached to a housing containing a gas cartridge and trigger mechanism, with the ampule contained within the sleeve during use. The sleeve must be separated from the housing to provide access to the ampule for replacement and/or filling. U.S. Pat. No. 4,338,980 to Schwebel et al. discloses a filling device for disposable ampules for use in jet injectors, but that device requires a special medicine vial as well as an ampule holder, a housing and a dispensing handle which a user must assemble in order to fill the ampule. Moreover, the device with its multiple parts is separate from the jet injector, and, thus, various parts of the device or the entire device may be misplaced between uses of the injector, particularly by those who are afflicted with poor vision or poor memory, such as elderly diabetics. There is thus a continuing need for a hypodermic injector combined with a precise, easily used ampule filling device in a single unit.
Ease of use for any patient-fillable ampule or jet injector is affected by the ease with which the user can read dosage indications during the filling process. Vernier scales, for example, are difficult for many people to read and understand, and other types of dosage indicators are hard to read for any patient with impaired vision. Such factors can reduce patient confidence in self-administration and, worse, can cause dosage errors.